SMAD3 or Mothers against decapentaplegic homolog 3 is a gene which appears in humans on chromosome 15. It is one of several human homologues of a gene which was originally discovered in the fruit fly Drosophila melanogaster. The name SMAD3 also refers to a member of the SMAD family of proteins.
SMAD3 or Mothers against decapentaplegic homolog 3 is a polypeptide that, as its name describes, is a homolog of the Drosophila protein "Mothers against decapentaplegic". It belongs to the SMAD family of proteins, which belong to the TGFβ superfamily of modulators. Like many other TGFβ family members, SMAD3 is involved in cell signalling. SMAD3 modulates signals of activin and TGFβ's.